The present invention relates to micro-electromechanical systems (MEMS) with integrated optical devices, in particular, to an assembly having micro-lenses integrated with MEMS actuators.
Optical communication systems increasingly require the use of lightweight and low-cost optical devices or subsystems. A large number of such optical devices or subsystems including optical transmitters and receivers used in prior art suffer from mediocre performance. Such optical transmitters or receivers are generally devised using micro-fabrication technologies with semiconductor and conductive material layers. However, the drive towards unprecedented functionality in such optical communication systems requires the seamless integration of micro-electrical, optical and mechanical components. The success of micro-electromechanical systems (MEMS) technology and general trends toward miniaturization of the optical devices or subsystems could significantly benefit optical communication systems. MEMS technology can meet the need for integrated optical devices or subsystems by using suitable semiconductor, insulator, and conductive material for multilevel layered miniature structures and interconnects. The deployment of MEMS technology, in optical communication systems, could allow fabrication of inexpensive optical devices in a batch process. Consequently, MEMS technology is poised to make a significant impact in the field of optical communications.
Although MEMS based optical devices are generally a fraction of cost, size, and weight of typical optical communication systems, they are significantly important for ensuring performance, reliability and affordability of such systems. Despite seemingly obvious advantages of MEMS technology for optical communication, enhanced MEMS fabrication methods are desired for new systems functionality. Regardless of the fabrication process employed, generally MEMS fabrication processes encompass three key features including miniaturization, multiplicity, and microelectronics. A typical MEMS fabrication approach includes a variety of deposition and etching steps that could be based on both wet and dry procedures that selectively add or remove material from a wafer. Among other things, however, the challenge is to provide an ease of fabricating and integrating MEMS components with micro-optical components both in monolithic and/or hybrid forms. Integrated micro-opto-mechanical components for optical communication systems including fiber-optic switches and/or optical interconnects can usher an optical communication revolution providing high bandwidth and speed increasingly desired for most advanced communication applications. For example, applications could include high bandwidth interconnect for high performance computer systems, reconfigurable crossbar interconnect for high bandwidth applications, streerable optical communication systems, and all-optical fiber crossbar switch.
At present, in a variety of optical communication systems, micro-optics elements such as reflective micro-optics elements are combined with micro-electromechanical systems (MEMS) to provide MEMS integrated micro-optical communication devices. Typically, such MEMS integrated micro-optical communication devices comprising reflective micro-optical elements suffer from several shortcomings. For example, in a variety of optical communication applications, it is difficult to micro-position various micro-optical elements for precise alignment of light beams or optical signals. Although the precision with which the micro-optical elements must be positioned varies according to a particular application, the micro-optical elements must oftentimes be aligned to within several microns to several tenths of microns. Typical applications that require such micro positioning include optical interconnect systems, laser communications systems, and free space fiber optic switches. For example, in free space fiber optic switches, alignment of a light beam or an optical signal emitted from an optical fiber is desired. More specifically, the alignment of the light beam of an input optical fiber, with another optical element is needed to perform free space beam steering of the light beam traveling through the input optical fiber. By appropriately micro positioning a micro-optical element relative to the input optical fiber or a laser diode, the light beam or optical signal provided by the input optical fiber or laser diode can be coupled to a respective optical fiber or a detector.
Unfortunately, for such optical communication systems, MEMS integrated micro-optical communication devices of the prior art have been limited in their abilities and applications. Furthermore, it is difficult to fabricate MEMS integrated micro-optical communication devices, which provide the desired ability to micro-position micro-optical elements for steering a light beam or an optical signal.
One technique for optical communication includes forming reflective micro-optical elements, such as micro-mirrors. Such prior art micro-mirror based micro-optical communication devices typically require numerous components to construct and operate, and hence are generally less reliable. In addition, most micro-mirrors based micro-optical systems require a multi-segment folded optical path that increases the size of the system. Therefore, in micro-mirrors based micro-optical communication devices, micro-mirrors can typically not be mounted in close proximity to optical sources, leading to less power efficiency and less compactness and reduced transmission distances.
Moreover, typical actuation force generators employed to selectively modify positions of the micro-mirrors, either in a reference plane or a selected direction, may not rapidly traverse a desired range of displacements for the micro-mirrors. In the absence of such capabilities, the utility and applications of MEMS integrated micro-optical communication devices having reflective micro-optical elements integrated with MEMS are significantly limited.
Accordingly, there is a need for improved micro-electromechanical systems (MEMS) integrated micro-optical communication devices suitable for beam forming and steering to enable optical communication including, but not limited to, an optical transmission, switching, and/or rapid alignment.
The present invention generally provides integrated micro-electromechanical systems (MEMS) and methods of fabricating and operating the same. In an exemplary embodiment, an integrated optical apparatus includes a micro-electromechanical member and a substantially transmissive micro-optical element coupled to the micro-electromechanical member such as a MEMS structure. The integrated optical apparatus may further include an actuator for operating the substantially transmissive micro-optical element to manipulate an optical output from an optical source disposed proximal to the micro-electromechanical member. The optical source may be in a coaxial alignment with the substantially transmissive micro-optical element such as a micro-lens. The micro-electromechanical member may be coplanar to the micro-lens, which may collimate or focus the optical output to form a light beam. The micro-lens may steer the light beam in a first selected direction responsive to an actuator input applied to the actuator. The actuator may selectively position the micro-lens in response to an actuating force for steering the focussed light beam in the first selected direction to form a steered light beam. The actuating force could be an applied voltage bias and an actuating force profile may determine the first selected direction and a position of the micro-lens. The actuator could be a comb drive actuator generally formed on a substrate. Such a comb drive actuator may include one or more fixed combs and one or more movable combs. The one or more movable combs may be displaced in response to the actuating force and they may include a frame to fixedly hold the micro-lens.
The comb drive actuator may further include at least one suspension member, each suspension member operably connected at a first end to the frame and at a second end to the substrate to generally suspending the frame. Selective positioning of the micro-lens may generally control a spatial alignment of the steered light beam. Moreover, the selective positioning of the micro-lens may be provided in a first displacement direction coplanar to a major surface of the micro-electromechanical member in response to a first type of the actuating force.
Alternatively, such selective positioning of micro-lens may be provided in a second displacement direction coplanar to the major surface of the micro-electromechanical member in response to a second type of the actuating force. In addition, the micro-lens may be positioned in a third displacement direction coplanar to the major surface of the micro-electromechanical member responsive to a concurrent application of the first type of the actuating force and the second type of the actuating force.
In an exemplary method of fabricating an exemplary integrated optical apparatus, a micro-electromechanical member such as a MEMS structure having an aperture may be formed. And a substantially transmissive micro-optical element such as a micro-lens may be interposed at the aperture generally provided in a micro-electromechanical optical assembly, which may be released to form the micro-electromechanical optical assembly. In one embodiment, the exemplary method of fabricating the integrated optical apparatus includes forming a first structural material layer over a substrate, a sacrificial material layer over the first structural material layer, and a second structural material layer over the sacrificial material layer. To form the micro-lens, an optical material layer having a major surface may be provided to fill in the aperture. The micro-electromechanical optical assembly may be further processed for adapting the major surface of the optical material layer into a spherical profile. Also, the micro-electromechanical member may be formed on a substantially transparent substrate.
In accordance with one aspect of the present invention, an exemplary optical communication apparatus may include an optical source to emit a light beam and a micro-electromechanical assembly such as a MEMS structure. The micro-electromechanical assembly may include a transmissive micro-optical element such as a micro-lens to receive the light beam for focusing and selective steering. And the micro-electromechanical assembly may be coupled to the optical source. The micro-electromechanical assembly may further include a comb drive actuator. Such comb drive actuator may be formed on a substrate to selectively position micro-lens in response to an actuating force applied to the comb drive actuator. Accordingly, the light beam may be steered to provide a steered light beam for an active alignment. Such active alignment may dynamically align the steered light beam in a selected direction in response to the actuating force. A feedback control loop may maintain a spatial alignment of the steered light beam. The micro-electromechanical assembly could be formed on a transparent substrate utilizing a deposition process, which may include forming one or more support layers. The optical source may be, but is not limited to, a laser diode, a fiber, a vertical cavity surface emitting laser diode, or an edge emitting laser diode. Likewise, the micro-lens may be, but is not limited to, a photo-polymer or polymer micro-lens, a glass or quartz micro-lens, or a semiconductor micro-lens. The micro-lens may be coplanar with a major surface of the micro-electromechanical assembly.
In another exemplary embodiment, the optical source may be an input fiber disposed in a fiber optical cross connect switch. A micro-electromechanical assembly such as a MEMS structure may perform switching of a light beam received at the input fiber to optically link the received light beam to a first output fiber of a plurality of output fibers disposed substantially facing the input fiber of the fiber optical cross connect switch.
In one exemplary embodiment, comb drive actuator may include one or more fixed comb, and one or more movable comb. The movable combs may be displaced in response to an actuating force such as an electrostatic force. The movable combs may include a frame to hold a micro-lens and at least one suspension member, each suspension member operably connected at a first end to the frame and at a second end to the substrate for suspending the movable combs.
In accordance with one aspect of the present invention, an optical communication apparatus may include a plurality of optical sources, each of the optical sources emitting a light beam, and a micro-electromechanical assembly such as a MEMS structure. The micro-electromechanical assembly may include transmissive micro-optical elements such as micro-lenses corresponding to each of the optical sources for focusing and steering the respective light beams generally received at the corresponding micro-lenses. And the micro-electromechanical assembly may be coupled to the plurality of optical sources. The micro-electromechanical assembly may further include a comb drive actuator. Such comb drive actuator may be formed on a substrate to selectively position the transmissive micro-optical elements in response to an actuating force applied to the comb drive actuator. Accordingly, the light beams may be steered individually or jointly to provide respective steered light beams for an active alignment. Such active alignment may dynamically align the respective steered light beams in a, selected direction in response to the actuating force. The micro-electromechanical assembly may be formed on a transparent substrate. A corresponding feedback control loop may maintain a spatial alignment for each of the steered light beams. The micro-electromechanical assembly could be formed on a transparent substrate utilizing a deposition process, which may include forming one or more support layers. The optical sources may be, but not limited to, a laser diode array, a fiber array, a vertical cavity surface emitting laser diode array, or an edge emitting laser diode array. Likewise, the micro-lenses may be, but are not limited to photo-polymer or polymer micro-lenses, glass or quartz micro-lenses, or semiconductor micro-lenses. The micro-lenses may be coplanar with a major surface of the micro-electromechanical assembly.
In another exemplary embodiment, each optical source may be an input fiber disposed in a fiber optical cross connect switch. A micro-electromechanical assembly such as a MEMS structure may perform switching of respective light beams received at associated input fibers to optically link the received respective light beams to a corresponding output fiber of a plurality of output fibers disposed substantially facing the input fibers of the fiber optical cross connect switch.
In one exemplary embodiment, comb drive actuator may include one or more fixed combs, and one or more movable combs. The movable combs may be displaced in response to an actuating force such as an electrostatic force. The movable combs may include a frame to hold micro-lenses and at least one suspension member, each suspension member operably connected at a first end to the frame and at a second end to a substrate for suspending the movable combs.
In accordance with one aspect of the present invention, an exemplary optical communication apparatus may include an optical source to emit a light beam and a micro-electromechanical assembly such as a MEMS structure. The micro-electromechanical assembly may be formed on a transmissive substrate substantially parallel to a horizontal plane. Such a micro-electromechanical assembly may include an electrostatic comb drive actuator having a micro-lens for focusing the light beam. The micro-electromechanical assembly could be coupled to the optical source for selectively steering the light beam. The electrostatic comb drive actuator may further include one or more fixed combs, each having a first set of fingers, and one or more movable comb, each having a second set of fingers which are in an interdigitized arrangement with the first set of fingers. The movable combs may be displaced within the horizontal plane in response to an actuating potential being applied to the electrostatic comb drive actuator. The movable combs may include a micro-lens frame to hold the micro-lens and at least one suspension member, each suspension member attached at a first end to the micro-lens frame and at a second end to the transmissive substrate for suspending the movable combs substantially parallel to the horizontal plane.
In accordance with another aspect of the present invention, an exemplary optical communication apparatus may include an optical signal sensing device for tracking the steered light beam such that the optical signal sensing device may provide a feedback signal to dynamically align the steered light beam.
In accordance with yet another aspect of the present invention, an exemplary optical communication apparatus may include a plurality of optical sources, each of the optical sources emitting a light beam, and a micro-electromechanical assembly such as a MEMS structure. The micro-electromechanical assembly may be formed on a transmissive substrate, which could be substantially parallel to a horizontal plane. The micro-electromechanical assembly may include an electrostatic comb drive actuator having an array of micro-lenses with each of the micro-lens corresponding to each of the optical sources for focusing the respective light beams to couple the micro-electromechanical assembly to the plurality of optical sources for steering the light beams.
The electrostatic comb drive actuator may include one or more fixed combs, each having a first set of fingers, and one or more movable combs, each having a second set of fingers which may be in an interdigitated arrangement with the first set of fingers. The movable combs may be displaced within the horizontal plane in response to an actuating potential being applied to the electrostatic comb drive actuator. The movable combs may include a micro-lens frame to hold an array of micro-lenses and at least one suspension member, each suspension member attached at a first end to the micro-lens frame and at a second end to the transmissive substrate, thereby suspending the micro-lens frame substantially parallel to the horizontal plane.
In accordance with another aspect of the present invention, an exemplary optical communication apparatus may include an optical signal sensing device corresponding to each of the optical sources for tracking the respective steered light beams such that optical signal sensing devices may provide a feedback signal corresponding to each of the optical sources to dynamically align the respective steered light beams.
In accordance with yet another aspect of the present invention, an exemplary method for optical communication may include the steps (a) receiving an optical input at a transmissive micro-optical element integrated with a micro-electromechanical assembly such as a MEMS structure; and (2) positioning the transmissive micro-optical element to steer the optical input received at the transmissive micro-optical element in a first transmission direction in response to a first actuating force such as a first voltage bias applied to the micro-electromechanical assembly for displacing the transmissive micro-optical element. The method may further include the step (c) steering the optical input received at the transmissive micro-optical element in a second transmission direction in response to a second actuating force such as a second voltage bias applied to the micro-electromechanical assembly.
In accordance with still another aspect of the present invention, an exemplary method for optical communication may include the steps (a) generating a light beam from an optical source, the light beam directed to a micro-lens integrated with a micro-electromechanical assembly such as a MEMS structure; (b) deriving from passing the light beam through a first major surface of the micro-lens a focused light beam; (c) applying an actuating force to the micro-electromechanical assembly for displacing the micro-lens in a first direction within a horizontal plane to steer the focused light beam; (d) receiving from a second major surface of the micro-lens a steered light beam directed to an optical detector in response to the actuating force applied to the micro-electromechanical assembly, wherein the second major surface of the micro-lens is disposed opposite to the first major surface; and (e) coupling the steered light beam to the optical detector for providing an optical link through free space between the optical source and the optical detector.
In accordance with still further aspect of the present invention, an exemplary method for fabricating an integrated optical communication apparatus may include the steps (a) forming a micro-electromechanical member such as a MEMS structure having an aperture; (b) forming a substantially transmissive micro-optical element interposed at the aperture to provide a micro-electromechanical optical assembly; (c) releasing the micro-electromechanical optical assembly; and (d) disposing an optical source proximal to the micro-electromechanical optical assembly. The step of forming the micro-electromechanical member may further include the steps (a) forming a first structural material layer over a substrate; (b) forming a sacrificial material layer over the first structural material layer; (c) forming a second structural material layer over the sacrificial material layer; (d) forming an optical polymer material layer having a major surface to fill the aperture; and (e) processing the micro-electromechanical optical assembly for adapting the major surface of the optical polymer material layer into a spherical profile determined through at least one parameter. In addition, the micro-electromechanical member may be formed on a substantially transparent substrate such as glass.
According to one feature of the present invention, a passive alignment of a MEMS lens assembly is provided for enabling an initial alignment of one or more optical sources with respect to associated one or more micro-optical elements. Accordingly, a flip chip module assembly technique is adapted for bonding the MEMS lens assembly to a carrier substrate, which receives the one or more optical sources. Likewise, a dynamic beam steering of one or more light beams generally carrying associated optical signals is provided for enabling an active alignment of the one or more light beams with associated one or more optical detectors. Preferably, a MEMS feedback servo loop can maintain the active alignment.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.